Technical Abstract:
Grasses are being championed as biomass sources for bioenergy production. Their ultimate use would be as a source of carbohydrate for fermentation to ethanol, conversion to oils via pyrolysis, or direct conversion to energy through combustion. In the latter case, increasing lignin content would enhance the energy density of the material, improving the net energy output. On the other hand, grasses with high lignin content are less efficient in terms of conversion to bioenergy in the form of ethanol. The unique acylation of grass lignins with p-coumarates (pCA) increases the energy output during biomass combustion. A spectrum of C3 and C4 grasses was evaluated for cell wall characteristics, including pCA and lignin content. Levels of pCA and the p-coumaroyl transferase (pCAT) responsible for incorporation of pCA into cell walls as pCA-monolignol conjugates were evaluated. Acylation of lignin by pCA ranged from 10.7 to 37.7 mg/g cell wall (CW), and lignin ranged from 163 to 222 mg/g CW. Corn and grain sorghum (both C4 plants) were the highest pCA and lignin grasses. Other C4 grasses fell more in line with C3 types. The pCAT activities did not follow the same pattern as the pCA incorporation into lignin. Some of the highest activities were found in C3 grasses having low pCA levels. Other important cell wall components (glucose and xylose) showed variable patterns dependent upon the individual grass species, but not consistent within the C3 and C4 groupings.